Television apparatus



Dec. 3, 1940. G. L. BEERs 2,223,983

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BLACK LEVEL 13 Snventor George L. Be ers Dec. 3, 1940.

G. L.. BEERs TELEVISION APPARATUS Filed May 28, 1938 2 Sheets-Sheet 2 (Mes/r VERT/CHL aww v'aow/ liwentor George L. Beers Lil Patented Dec. 3, 1940 y'aaaaess f TELEVISION APPARATUS George L, Beers; HaddonfieldfN, J., assigwnor` to:`

Radio Corporation ofAmerica, a corporation of Delaware Application May 28,1938, serial No. 210,587 f -Y iciaims. (C1. iis-7.7)

invention relates to cathode ray tube apparatus andmore particularlytotelevision transmitters and receivers ofthe type utilizing `cathode s. Intelevision,transmitters* and receivers, in par- 1 ticular, it is the practice to deflect a cathode ray horizontally at a high frequency and vertically atacomparatively low frequency wherebyv the screen surface such as the 'mosaic of thetransmitter tubeor the fluorescent screen oi the receiver tube is scanned. Preferably, both the horizontal deection and the Vertical deection are eiected by means Vof saw-tooth Waves.

Regardless of the shape of the deflecting waves, i

there are produced on the screen surface unden r sirable return traces for both the horizontal and the vertical deflection unless "suitable precautions `are taken.

l It,is, according1y, theobject of my invention to provide a novel method of and means for eliminating the above-mentioned return traces.

' f In .practicngmy invention, the cathode ray,

`such as deecting plates and supplying special y embodiment of my invention,

after it has been deflectedlacross the screen surface, is deflectedl away from the immediate vicinity,y of the screen surface during the return line period whereby the return trace is oi the screen. This may be accomplished by providing the cathode ray tube with additional-deflecting means deflecting waves vsuch asrectangular deecting wavesto such deflecting means. t r

The invention will be better understood by referring to the `following description taken in connection Awith the` accompanying drawings' in which Figure 1 "is afschematic diagram showing one Figures 2, 2a, 3 and 3a. are

y referredto in explaining the invention,

Figure 4 is a view showing how the return traces maybe masked olf,

' .'*Figur'es 5 and 5a are other curves which are referred to, in explaining the invention, v

Figurelvfis a `view showingthe scanning pattern produced by one embodiment of my; inventioavand 1;. Figure 7 is a view showing the scanning pattern reduced. by another embodimentof my invenn..

i pliedlto;atelevision receivercomprising a cathode raytub'e which 'preierabiy is of thezhighiy evacuatedtype having therein. an indirectly heated cathode 2, a control'electrode 3, ay iirst anedell and a second'lanode lig;rv 'tIhe cathode ray curves .which are c eie'iiig: to Fig." 1, my invention is* shown1 apa indicated'` at 'l ,preferbly' is ,electrostatically focused in a Well known manner. c,

f The cathode ray tube is provided with a suitable deflecting yoke V whereby the cathode ray lmay be caused to scan a screen surface such 5 as afluorescent screenS on the end of Vthe tube envelopeuy Picture signals and; synchronizing impulses are suppliedto the control electrode 3 throughan amplifier tube Il. It maybe assumed for the purpose of illustration that this composite signal l comprising gpicture signals and synchronizing impulses has been generated in accordance With-,the 'teachings nofi the Vance British Patent 395,499.l A signal of this type is illustrated in 1iig.' 2 1,I

yWhere thepicture signals are indicated at Vl2 and the horizontal synchronizing impulses at |13.

In Fig. 2a thevertical,synchronizing or fram- L The horizontal synchronizing impulsesand the framing. impulses have Vsubstantially the same' amplitude v(an yamplitude corresponding` to' blacker than black,L for example), theoframing impulses being of longer duration than ythe horizontal synchronizing impulses to facilitate frequency separation ofA the two groups of, synchronizing impulses. It may be noted at this` point, however, that my inventionis especially applicableto a system in which the synchronizing irnpulses have a polarity in the direction of white.. The composite signal .is also supplied over a conductor i6 to a suitable separating circuit Il which removes the picture signals from the synchronizing--impulses and which also separates the horizontal synchronizing impulses from the vertical synchronizing impulses. The separating circuit may be ofy the typefdescribed and claimed, in' Patent'Nl.v 2,207,839, Vissued July 16, 1940, in the nameof William A. Tolson andy assignedto Radio Corporationr of America.

described in Tolson et al. Patent 2,101,520, dated December 7, 1937.

The yoke 8 preferably is of the type described and claimed in Patent No. 2,167,379, issued July 25, 1939, in the name of William A. Tolson and assigned to Radio Corporation of America.

By referring to Figs. 2 and 2a., it will be seen that it is proposed to omit blankingsignals from the composite signal whereby the cathode ray tube will not be driven tc cut-off to block the cathode ray during the return line period; that is, comparing the curves of Figs. 2 and 2a where the curve in Fig. 2 represents the horizontal deilecting saw-tooth wave, it will be seen that the deflecting plates, preferably is an impulse volt-A agey 21 such as shown in Fig. 3a. This impulse occursr duringthereturnline period as will be seen by comparing the curves of Figs. 31 and 3a, the curve in Fig. 3 representing the horizontal saw-tooth deflecting wave. As a result, the cathoderay 'l is caused to-trace a path of a character indicatedby the dottedlines 28 on the end of the i cathode ray tube.

Referring to the dotted line trace 28, it will be seen that at the end: of each scanning line the cathode ray 'l is deiiected below the bottom of the fluorescent screenY S'whereby the return trace isbelowthe screen surface. return trace, the cathode ray is deflected upwardl'yrto the proper position to begin the next scanning line. Thus, it will be evident that there i`s-no return trace on the screen surface.

The auxiliary deflecting impulse 2'!V may be generated in a variety of ways but since, for a cathode raytube of the type illustrated, it should be of rather large amplitude, it preferably is generat'ed'y by means of a blocking oscillator 3| and a- .2 suitable wave-shaping circuit indicated at 32..

The blocking oscillator 3| maybe designed as taught-in the above identified Tolson et al.patent. Preferably, the" gridl circuit of the blocking oscillator is connected through a conductor 33 and a I switch-34 totheconductor I8 which supplies horizontalsynchronizing impulses. With this circuit connection; the horizontal synchronizing impulses trigger off the blocking oscillator whereby voltage impulses of great amplitude appear in its output circuit. These impulses are passed through thewavesshaper 32 which* reshapes' the blocking oscillator impulses to produceA the rectangular impulses 27'. ItI will be understood that the wave shaper 32 may include clipping tubes and anyl other circuit elementsnecessaryV for producing the` rectangular impulses 27 as is well known inthe art.

As" indicated in Fig. 4, a mask may be placed overY the end of the cathode ray tube I to mask off the lines caused by the return line traces of the cathode ray T in the .event that the iluorescentA material covers the entire end of the cathode ray tube envelope instead' of being confined' to the area indicated by' the reference numeral 9. i As a matter' oi fact, the' return deection is so At the end of thefast that the return line trace will be faint as compared with the scanning lines.

Instead of controlling the blocking oscillator 32 by means of the horizontal synchronizing impulses it may be preferred to utilize a conducting strip 35 which is struck by the cathode ray at the end of each scanning line. Each time the cathode ray strikes the strip 36 an electrical impulse is transmit-ted over the conductor 37' and through the switch 34, which now is in the dotted line position, to the blocking oscillator 3| whereby the impulse 27 is produced to deflect the cathode ray below the screen surface during the return line period.

So. far there has been described only the means for eliminating the v return line trace caused by the horizontal deilection. The return line trace of the vertical deection may be eliminated in a similar manner by .employing deflecting means such as the deflecting plates 38 which are positioned to deflect the cathode ray at right-angles tothe deflection caused by the plates 261. The deflecting plates 33.V have applied'thereto-rectangular voltage impulses occurring at the :frequen-- during the vertical return line period. They maybe producedrat the proper frequency by means ofa blocking oscillator 4| and a wave-shaping circuit 42, these units preferably being of a design corresponding to the design of' units 3| and 32, respectively.

The-blocking oscillator 4| is connected throughy al conductor 43 to the conductor 2| whereby vertical synchronizing impulses are supplied thereto for the purpose of triggering. off thebl'ocking oscillator at the endof each picture frame whereby the cathode ray is deflected to one side of the screen 9 during the vertical4 return period. As a practical matter, thedeflection caused by the plates 38 during the vertical return 'period would probably be sufficient to deflect the cathode ray 'l against the neck or side of the cathode ra-y tube envelope. If this were not the case, however, and if, also, the cathode ray were not deected against the neck of` the' tube bythe plates 26-s as would probably be the case, the complete pattern traced' by thecathode ray would be as shown inV Fig. 6. For the purpose of simplifyingY the diagram, only four scanning lines have been indicated. It will be seen that the rst scanning line, line No. 1i moves to the right across thescreen 9 andisthen deflected vertically and downwardlyV Where itL is held during the return line trace la. This action is repeated for successive scanning lines, the lines 2, 3- and 4 representingv the additional scanning'v linesand the lines 2a, 3a and 4a' representing. the correspending return' linetraces. It willbe seen` that at the end of the picture, frame, thatjis; at the end of the scannnig line 4, the cathoderayis deflected toone side-of the screen' 9; whereby the vertical return line traces 4a, 5 and 5a areoi the screen surface.

In the diagram shown' in Fig; 6, thev defl'ecting plates 26 continue to be effective during thereturn.line` trace. There is no objection'to this but itcanbe avoide'cliby feeding theimpulse 39Whi`ch appears in the output of"V the wave-Shaper 42 through a conductor' 44 and' a' switchy 46 tothe grid of the blockingA oscillator 3|' whereby itis blocked' or rendered inactive' during the vertical' y tern traced by the cathode ray 1 is that shown in j Fig.7.

It will be understood ,that the r apparatus inustrated in Fig.4 1 may befmodiiied in various ways without departing from the spirit and the scope yof the invention. For example, the delecting plates 26 and 38 may be vreplaced by suitable electromagnetic deflecting means., ,If desired, such deflecting means may be combined with the deiiecting yoke 8. Or, if preferred, deflecting plates corresponding tok plates 26 and 38 may be incorporated in the cathode ray tube as part of the gun structure whereby the deecting voltages applied thereto may be of relatively small ampli-v tude. It should be understood that my invention applies equally well to television transmitter tubes where, in place of a fluorescent screen 9, there is a mosaic of photoelectric elements, or the like.

It should also be yunderstood that my invention is especially adapted for use in a system where the picture signals and the synchronizing signals are transmitted. overv separate channels. In such a system the picture signals only would be applied to the control electrode 3 of the cathode` ray tube while the synchronizing signals would be applied to a circuit corresponding tothe separating circuit I1. Where a composite signallconsisting of picture signals and synchronizing impulses is transmitted, my invention makes it possible to reverse the polarity of the synchronizing impulses with respect to the polarity shown in Fig. 2a. In other words, the synchronizing impulses may be impressed upon the control grid with a positive polarity and the return line traces still avoided in accordance with my invention.

It will be apparent that various other modifications may be made inmy invention without departing from the spirit and scope thereof and I desire therefore that only such limitations'shall be placed thereon asare necessitated by the prior art and are set forth in the appended claims.

I claim as myinvention:

ing device to produce a useful deflection and al return deiiection, an additional deflecting device for'deilecting said ray vertically, asecond additional deflecting device for delecting said ray horizontally, means for impressing a deflecting wave upon said iirst additional deecting device during each horizontal return deflection, and

1. In combination, a cathode ray tube having therein a certain screen area to be scanned and means for impressing a deilecting wave upon said second additional deflecting device during each vertical return deflection, said last two deflecting waves having sufficient amplitude to hold said ray off said screen areal during said return deflections.

2. In combination, .a cathode ray tube having therein a certain screen area to be scanned and including means for producing ak cathode ray,`

a deflecting device for deecting saidray in one direction, means for impressing a deecting wave upon said deflecting device to produce a useful deflection and a return deflection, an additional deecting device for deecting said ray in a direction substantially at right angles to said one di. rection, and means for impressing a deecting wave upon said additional deilecting devicedur-` ing each return deflection, said last delecting wave having suilicient amplitude to hold said ray j off said screen area during said return deflection, wherein said first deiiecting wave has a sawtooth wave form and wherein the deflecting wave impressed upon said additional dei'lecting device is approximately rectangular in shape.

3. In combination, a cathode ray tube having therein a certain screen area to be scanned and including meansfor producing a cathode ray, a deecting device for deilecting said ray in one direction, an auxiliary deecting device for deflecting said ray in a direction substantially at right angles to said one direction, means corn prising a deflecting Wave generator for impressinga deecting wave upon said first deilecting .device to produce a useful dellection and a return deflection, means comprising a blocking oscillator for impressing a deflecting wave upon said additional deecting device during said return deilection, and means for impressing synchronizing impulses upon both said deiiecting wave genera` tor and said blocking oscillator.

4. In combination, a cathode ray tube having therein a certain screen area to be scanned and including means for producing a cathode ray, a deflecting device for deflecting said ray in one direction, an auxiliary deflecting device for deyfleeting said ray in a direction substantially at right angles to said one direction, means cornprising. a deilecting wave generator for impressing a deilecting wave upon said rstdeflecting device to produce a useful deflection and a return deilection, means comprising a blocking oscillator for producing a deflecting wave and impressing it upon said auxiliary deflecting device, a conducting strip adjacent to said screen area, and means comprising a connection from said conducting strip to said blocking oscillator for causing said blocking oscillator to produce the second mentioned deflecting wave during said return de'-` flection. y

GEORGE L. BEERS. 

